// 3.静态常量
static mut MY_AGE:i32 = 30;

fn main() {
    // 1.常量定义
    const SECOND_HOUR:usize = 3_600;
    const SECOND_WEEK:usize= 7 * SECOND_HOUR;
    println!("WEEK is:{SECOND_WEEK}");
    // 2.常量生命周期可见性在块级作用域中
    {
        const ZH:i32 = 1000;
    }
    // not found in this scope
    // println!("zh is:{ZH}");

    // MY_AGE += 1;
    
    // 4. unsafe中修改静态变量
    unsafe {
        MY_AGE += 1;
        println!("new MY_AGE is:{MY_AGE}");
    }
}
